1. Field of the Invention
The present invention relates to a Connection Admission Control (CAC) method and apparatus in a Broadband Wireless Access (BWA) system, and in particular, to a CAC method and apparatus in a BWA system whereby whether to admit or deny connection is determined by converting a transmission request rate into the number of required slots to be compared with the number of available slots.
2. Description of the Related Art
In a wireless access system, when limited network resources are distributed to a plurality of Mobile Stations (MSs), the number of access connections (or the amount of traffic) must be restricted to ensure Quality of Service (QoS). To this end, Connection Admission Control (CAC) is used to determine whether to admit or deny connection in response to an access request (hereinafter, a ‘connection admission request’) in consideration of currently available resources.
FIG. 1 is a view for explaining a general concept of CAC.
According to a general CAC algorithm, when a connection admission request 101 is received from an MS for a specific service, a wireless access system 102 examines an available channel capacity 104 (having the same unit as a bandwidth or a transmission rate). Then, a CAC process 103 is performed in such a manner that the available channel capacity 104 is compared with a transmission request rate of a connection that requests connection admission and if the transmission request rate is less than the available channel capacity, the connection is allowed, otherwise, it is denied.
A Broadband Wireless Access (BWA) system (also referred to as a mobile World interoperability for Microwave Access (WiMAX) system) based on the Institute of Electrical and Electronics Engineers (IEEE) 802.16e Wireless Metropolitan Area Network (WMAN) employs a next generation wireless communication technique. With this technique, not only voice service but also various multimedia services (e.g., Internet access, high-speed data transmission, video, etc.) can be provided at any time or location through use of a portable terminal. In addition, a data service can be provided at a higher transmission rate than the transmission rate of the conventional cellular mobile network.
In the BWA system, the available channel capacity continuously changes for the following reasons: multi-path fading and shadowing, a time-varying channel condition of a portable terminal, and a movement speed. Furthermore, signaling overhead (e.g., MAP information) varies depending on the number of users accessing the BWA system; and the available channel capacity is enhanced using Adaptive Modulation and Coding (AMC), Hybrid Automatic Repeat reQuest (HARQ), Proportional Fairness (PF) scheduling, or Automatic Repeat reQuest (ARQ).
Therefore, estimating the available channel capacity is one of the most important factors in determining the admittance of a connection request.
However, the CAC algorithm used in the conventional Code Division Multiple Access (CDMA) network or the conventional Global System for Mobile communication (GSM) network is not easily applied to the BWA system because the BWA system employs an Orthogonal Frequency Division Multiple Access (OFDMA) scheme, and thus its multi-channel operation method is different from that of the conventional wireless network.
In the BWA system, a Real Time (RT) service connection must be differentiated from a Non Real Time (NRT) service connection. Further, a new connection must be dealt with in a different way from a handover connection.
In the BWA system, a MAP records the information on resource allocation in a two-dimensional domain composed of a time domain and a frequency domain. Along with an increase in the number of users, MAP overhead increases. This feature must be taken into account in designing the CAC of the BWA system.
Accordingly, there is a demand for a CAC method and apparatus in a BWA system, whereby an RT service connection is differentiated from an NRT service connection, a new connection is differentiated from a handover connection, and MAP overhead must be taken into account